Comparative analysis of onychomycosis in Puerto Rico using molecular and conventional approaches

Onychomycosis is the most prevalent nail ailment in adults, accounting for 50% of all nail infections. Dermatophyte fungi are the primary cause, but non-dermatophyte molds (NDM) and yeasts can also cause onychomycosis. It remains important to precisely determine the fungal cause of onychomycosis since the response to current treatments may vary between fungal classes. Real-time polymerase chain reaction (qPCR) has become a widespread tool for detecting fungal organisms for diagnosis due to its sensitivity and ability to detect down to the species level. This retrospective study aims to evaluate the qPCR Onycho+ test for dermatophyte detection using remnants of toenails from a cohort of patients from Puerto Rico.  Two hundred forty-two toenail samples submitted for histological examination via Periodic acid Schiff (PAS) staining for suspected onychomycosis were analyzed by the Onycho+ test and Sanger sequencing of the internal transcribed spacer (ITS-2). Compared to the gold standard Sanger sequencing method, the Onycho+ test reported an agreement of 91.39%, a sensitivity of 100% and a specificity of 84.5% in detecting dermatophytes, superior to the histology method which had a 69.53% agreement, 85.1% sensitivity and 57.1% specificity. The distribution of fungal organisms detected in this cohort shows a dermatophyte majority but a higher-than-expected proportion of NDMs. Nails negative for the Onycho+ test and positive for histology were mostly NDMs. This study demonstrates that the clinical performance of the Onycho+ test is superior to histology in detecting dermatophytes and that a combination of Onycho+ and histology can result in a higher clinical accuracy.